This invention relates generally to automotive emission control valves and systems, such as exhaust gas recirculation (EGR) valves that are used in exhaust emission control systems of automotive vehicle internal combustion engines. More specifically, the invention relates to an improvement for measuring the gas flow in an emission control valve and/or system via pressure sensing ports on opposite sides of an orifice.
Commonly owned U.S. Pat. No. 6,116,224 (Cook and Busato) discloses an EGR system comprising an EGR module. One element of that module is a pressure sensor that senses pressure differential across a circular orifice through which exhaust gas flow is constrained to pass when a valve of the module allows flow to the engine intake system.
A circular orifice of given diameter possesses a known relationship between flow through the orifice and pressure drop across the orifice. In other words, flow through the orifice, and hence flow through the module, can be calculated by measurement of pressure drop across the orifice and applying the known flow/pressure drop relationship to the pressure drop measurement. U.S. Pat. No. 6,116,224 shows various embodiments for communicating the pressure drop across the orifice to the pressure sensor.
U.S. Pat. No. 5,613,479 discloses an EGR system that uses a similar general principle for measurement of EGR flow. Sensing port taps sense pressure difference across an orifice through which exhaust gas flow is constrained to pass. The orifice is disposed in a straight section of pipe that is provided with openings in its side wall at opposite sides of the orifice. An end portion of a sensing port tube is fit to a respective opening such that a tip of the end portion protrudes slightly into the pipe. The tip end of each sensing port tube is necked down to create at the tube entrance a restrictor having a diameter less than the nominal diameter of the tube. The restrictor thereby forms an orifice as the tube entrance. Each sensing port tube is connected through a rubber hose to a differential pressure sensor. The restrictors are said to reduce audible noise emanating from the EGR system as a result of exhaust pulsations transmitted through the rubbers hoses.
One generic aspect of the invention relates to an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through the first port is communicated through a flow restrictor proximate the flow path that imposes a greater restriction on the communication of the flow path to the first pressure reading port than any restriction imposed on the communication of the flow path to the second pressure reading port.
A further generic aspect relates to an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through one of the ports to the corresponding pressure reading port is communicated through an orifice that faces the orifice in the flow path.
One more generic aspect relates to an exhaust gas recirculation valve comprising a valve body for conveying exhaust gas from an exhaust system of a combustion engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through one of the ports to the corresponding pressure reading port is communicated through an orifice that faces the orifice in the flow path.